Can a Glamour bard maintain concentration on another spell while using Mantle of Majesty? [duplicate]

Question

According to the text of Mantle of Majesty (a Bard College feature from the College of Glamour, Xanathar's Guide to Everything, page 14):

As a bonus action, you cast command, without expending a spell slot, and you take on an appearance of unearthly beauty for 1 minute or until your concentration ends (as if you were concentrating on a spell).

Specifically, the "as if you were concentrating on a spell" part bothers me. According to the rules, the things that can cause you to lose concentration are:

• Casting another spell that requires concentration. You lose concentration on a spell if you cast another spell that requires concentration. You can’t concentrate on two Spells at once.

• Taking damage. Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon’s breath, you make a separate saving throw for each source of damage.

• Being incapacitated or killed. You lose concentration on a spell if you are incapacitated or if you die.

Class features are not spells. So, does this mean that if you cast a concentration spell and then use Mantle of Majesty, you can concentrate on both as long as you don't take damage?

Answer 1

No, not without breaking concentration on Mantle of Majesty

Here is clarification from Xanathar’s Guide to Everything:

CONCENTRATION

As soon as you start casting a spell or using a special ability that requires concentration, your concentration on another effect ends instantly.

Whilst Mantle of Majesty may not be a spell, it is a special ability which requires concentration, thusly casting a spell (or using another ability) that requires concentration causes your concentration to break.

The “(as if you were concentrating on a spell).” is an attempt at clarifying this.

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Also, for added clarification from my own comment below this answer:

Mantle of Majesty is described as an ability: “At 6th level, you gain the ability to cloak yourself in a fey magic that makes others want to serve you.” Whilst its description doesn't use the word special ability, PHB page 45 says this about classes: “Your class gives you a variety of special features, such as a fighter's mastery of weapons and armor, and a wizard's spells.” From this we can infer that Mantle of Majesty is a special ability.

Answer 2

If you cast a concentration spell, then your appearance as an unearthly beauty ends.

You cite all the relevant rules and answer your question yourself.

you take on an appearance of unearthly beauty for 1 minute or until your concentration ends (as if you were concentrating on a spell).

"As if you were concentrating on a spell" makes this explicit. This feature specifically follows the rules as if it was a concentration spell, which features generally aren't. Specific Beats General (PHB 7).

If you cast a concentration spell, then your appearance as an unearthly beauty ends. Any other of your previous concentration abilities or spells also end if you use Mantle of Majesty.

XGtE makes this even more explicit in its section about concentration.

As Mantle of Majesty (XGtE 14) is an ability:

At 6th level, you gain the ability to cloak yourself in a fey magic that makes others want to serve you.

then the Concentration (XGtE 5) section applies:

As soon as you start casting a spell or using a special ability that requires concentration, your concentration on another effect ends instantly.