Extracting Last names only from a cell of contacts

[linaeum66]

<style type="text/css"><!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--></style>Hello, I am looking for a formula to convert a full name in the various formats seen below and convert them all to a consistent "last name only" cell in an adjacent column. I've been trying myself for a while, but am not making much progress. Does anyone know how to do this?
Thanks so much@

Full name		Last Name
John Doe		Doe
Doe, John		Doe
John D. Doe		Doe
John Doe MD		Doe

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[Peter_SSs]

I suspect there will be other formats for which all or most of the suggestions will fail, but for those formats provided so far, here is yet another.

Excel Workbook
	A	B
1	Full	Last
2	John Doe	Doe
3	Doe, John	Doe
4	John D. Doe	Doe
5	John Doe MD	Doe
6	John Doe PhD	Doe
7	John Hill PHD	Hill
8	Sam Withers	Withers
9	Jones, Michael John	Jones
Last Name