My wife saw this the other day in a seminar handout.

Problem:
The word “apart” — spelled A-P-A-R-T with no spaces — does not belong in this phrase.

Explanation:
The word “apart” as an adverb means into parts or pieces, as in “The tornado blew the house apart.”

The word “apart” can be combined with “from” to form a prepositional idiom that means besides or in addition to, as in “She wrote to no one apart from Jim.”

The word “apart” as an adjective means having unique or independent characteristics and is usually used after the noun that it modifies, as in “an institution apart”.

The word “apart” is NOT a noun, but a noun is what the phrase required, given that the writer was referring to someone not being a member of a group.

Solution:
“… no longer a part of the group”