Compare file names on directory

Dears,

Would you please help on following bash script:

I want to get the most recent file named alfaYYYYMMDD.gz in one directory:

for example:

in directory /tmp/

ls -ltr
alfa20130715.gz
holding.gz
alfa20130705.gz
sart.txt
merge.txt.gz
alfa20130802.gz

my result shoud be alfa20130802.gz ( created in 2013-08-02)

Thank you in advance

$ head -1 <(ls -r alfa*)
alfa20130802.gz

$ tail -1 <(ls alfa*)   
alfa20130802.gz